Vehicle Fires: how they start, spread, and how to prevent them

Automobile fires are often preventable if the right risk mitigation measures are taken, and proper maintenance is followed. However, it’s important to be aware of the common causes of vehicle fires and how to prevent them. We asked Sovereign’s Don Mann, Risk Specialist, all of our burning questions (no pun intended) about vehicle fires – what causes them, how they spread, and most importantly how to prevent them. 

Don has over thirty years of experience in fire services and retired as an Operations Captain. He is NFPA 921 Fire and Explosion Investigations certified. Over his several years in fire operations he has attended to many single and multiple fire incidents and subsequently rendered investigative determinations on cause and origin.

What are the common causes of vehicle fires?

Many of the common causes of vehicle fires that I’ve witnessed over my career mirror those noted by Micheal Wood, a captain at Toronto Fire Services. He identifies the following¹ :

• Fuel system leaks: Rotten fuel lines; faulty fuel line connectors; leaky fuel injection system
• Electrical system failures : Faulty car battery; broken lightbulbs; short circuits; the breakdown of fuses, fusible links, and circuit breakers
• Mechanical failures: Faulty design in the vehicle or improperly installed device
• Heat source: Overheated engine due to worn-out water pump or cooling fan; heat from powered equipment; smoking and driving; hot or smoldering objects
• Aftermarket accessories: Installations not carried out by authorized technicians can inadvertently introduce an electrical fault and cause a fire
• Catalytic convertors: Catalytic converters can be a magnet for road debris that catches on the converter’s heat shield and burns; if clogged or overworked, it can easily overheat
• Rodents/animals: Nests that act as kindling; stashes of nuts; soy-based wire insulation that attracts rodents to chew through the wiring
• Dangerous cargo: Propane tanks and gasoline jerry cans can fuel a fire in the event of a collision; transporting or storing toxic chemicals in vehicles not designed for the task
  
  

While there are several potential causes, and it’s not entirely uncommon for the cause to be deemed ‘undetermined’ following investigations, it’s still critically important to carry out a thorough investigation to understand the cause of the fire and ensure the future safety of your fleet, drivers, and others on the road.

For example, there was a recent example of a claim where the cause of fire was determined to be a defective block heater, and the fire occurred prior to the insured receiving a recall notice from the manufacturer. In this case, a forensic fire investigator was able to determine the cause, which was invaluable evidence along with the subsequent recall notice to be able to successfully recover the financial loss from the manufacturer.

In my experience, it’s very seldom that vehicle manufacturers accept liability, and this was one of those rare cases that was supported by a strong investigation and the preservation of evidence. There have been claims investigations for fires that ultimately do result in a manufacturer issuing a recall and this reinforces the necessity of a thorough claims investigation to recover not only for existing claims but also to protect against future claims to protect the public at large from property damage, injury, or death. 

What ignites first in a vehicle fire?

I could speculate based on my experience, but it’s best to look to the data to answer this question. According to Highway Vehicle Fires data² , most items that first ignite fall under the category of ‘general materials’, which includes tires, insulation around electric wire and cables, trash, and fabric. The most common item to initially ignite is insulation around the electrical wiring, or cables. Unsurprisingly, the second leading category of ‘items first ignited’ is liquids, piping, and filters, which include fuel in various locations throughout the vehicle. 

In your experience, is it common for engine fires to spread to the fuel tank? 

I have never been involved in a case where the fire has spread to the gas tank. Typically, gas tanks are located at the rear of the vehicle, however considering that today most gas tanks consist of plastic, this could be viewed as an exposure potential. 

It’s worth noting that with the rise of electric and hybrid vehicles, there are more batteries located behind rear seats and in trunks, along with the associated wiring that travels within the rocker panels and other areas of the vehicle. In the case of an electrical system failure, these wires could spread fire throughout the vehicle. 

If so, does the type or size of gas tank affect the potential exposure? 

The type or size of gas tank doesn’t necessarily affect the potential exposure, however since most gas tanks today are comprised of plastic, this raises potential for general concern. 

When there is a vehicle fire, is the fire typically contained to the vehicle, or does it tend to spread to other vehicles or buildings? 

Typically, a vehicle fire stays contained to the vehicle. However, if the subject vehicle is located in close proximity to another vehicle, then there is potential for radiant heat to affect other exposed vehicles, leading to deflagration. 

When it comes to accumulated exposures, it is common for large industrial companies to store their vehicle in the yard, parked side by side. As we’re well aware, vehicles contain both flammable/combustible liquids (gasoline, oils, antifreeze, etc.) and highly combustible materials (upholstery, plastics, etc.) which when exposed to fire can very quickly spread, causing a 100% loss expectancy. 

Are you familiar with any situation where a fire started in a vehicle and spread to the building that the vehicle was parked in? 

I have been involved with vehicle fires where the vehicle was in close proximity to a structure where radiant heat damaged some exterior siding materials. I have also seen a situation where the subject vehicle was located in a garage and led to the extension of fire to the interior of the building. 

Based on your experience, are specific vehicle types more susceptible? 

Not necessarily. However, electric and hybrid vehicles, due to the level of electronics and electrics within the vehicle’s design, can tend to have greater fire development potential resulting from electrical failure and fire developing due to arcing. 

Do vehicle fires tend to happen mainly when a vehicle is running, while warming up, or after it has been shut off from being in use? 

My experience seems to indicate that vehicle fires generally occur during the use of the vehicle and after the vehicle is shut down after being used. 

What are some recommendations to help prevent vehicle fire losses?

When storing vehicles in your yard/compound for extended periods of time:

• Eliminate as much fuel from the tank 
• Disconnect the battery or install kill switches or devices that disconnect the power supply from the batteries to the vehicle systems when the vehicles are parked overnight.
• Separate your compound into two areas to store vehicles that are parked vs. in use. 
• Restrict a large accumulation of units stored together in one large group. Maintain smaller groups of vehicles and provide a clear space between groups (minimum 25 ft if possible). Large fleets should be kept at a minimum of one empty parking space every five units, when possible, to help firemen stop the spread of fire.
• Do not store accumulations near building structures – store as far away as possible – ideally 50 ft clearance.
• Install recordable surveillance cameras to monitor your exterior yard. 
• Engage in physical security patrols in rural and industrial areas
• Make sure vehicle keys are secured inside the building but accessible so they can be accessed quickly in the event of a fire, and so that the units not involved can be moved/relocated.
• Ensure local fire services are aware of your emergency response plan and keep a spare key to the vehicle lock box in the fire department’s lock box, located at an offsite location and chosen by the fire department.

Fire prevention is just one of the many ways to protect your fleet, drivers, and your property. Check out the Auto Risk Management Toolkit for helpful resources to protect and support your drivers and help prevent road risks before they happen. 

¹Nine common causes of car fires. (2018, January 3). Retrieved March 25, 2021,
²Highway Vehicle Fires (2014-2016). (2018). Topical Fire Report Series, 19(2).